266 J. E. WODSEDALEK. 



side of it. By illuminating that side of tin- paper they soon 

 crawl upon tin- top which is shaded. Then, when the strong 

 light is again thrown from above, they move below, and in that 

 manner can be made to nn>\e back and forth repeatedly, though 

 not with Mieh precision after the experiment is kept up for some 

 time. The nymphs respond to light most readily when occupying 

 the upper sjdi- of tin- paper, and the best results are obtained 

 \\hen white paper is used. Ouite similar results are obtained 

 b\ using gray or black paper, but in such cases the nymphs lake 

 a much longer time to move trom one surface to another. 



I have performed quite a number of series of experiments with 

 different groups of nymphs using two lights, differing in intensity, 

 one at each end of a glass basin twenty-four inches long. I 

 noticed that by placing the nymphs in the 1 water half way between 

 the two lights they would often continue going in the direction 

 in which they first started, regardless of the intensity of the light, 

 though many of them manifested much promptitude in going 

 towards the end of the dish from whence came the light of less 

 intensity, even when there was a difference of only a few candle 

 powers. The excitability apparent in many specimens at the 

 instant of being placed in the water, which is largely responsible 

 for their reckless behavior was almost totally reduced by placing 

 the nymphs in a narrow tunnel made of glass strips, which was 

 placed in the middle of the large basin at right angles to the rays 

 of the two lights. The tunnel was sufficiently wide to enable 

 the specimens to go forward, but not wide enough to enable 

 them to turn around in it. Then the nymphs were put in at 

 one end and allowed to pass through two or three 1 inches of the 

 tunnel, thus getting the full force of the two lights at the same 

 time, and also a chance to resume a more normal attitude, Uy 

 the time the end of the tunnel was reached, which was in line 

 with the two lights, it was only a mat ter of choice which direction 

 was to be taken. Sometimes the nymphs would manifest no 

 choice, but remain in the middle ot the dish for several minutes, 

 especially when the two lights differed little in intensity. Hut, 

 generally the insects exinced considerable precision in choosing 

 the end of the basin from which came the light of less intensity. 

 The results obtained in some o| the experiments are given in the 

 following tables. 



